My invention comprises improvements in powertrains for automotive vehicles, particularly automotive vehicles with unitary engine and transmission assemblies.
In the case of front-wheel drive vehicles, it is common practice to mount an internal combustion engine in transverse disposition with respect to the fore-and-aft center axis of the vehicle within a forward engine and transmission compartment. Multiple ratio planetary gearing is used to deliver torque from the engine to axle half-shafts disposed in generally parallel disposition with respect to the engine axis. An example of an arrangement of this kind is the transaxle assembly disclosed in U.S. Pat. No. 4,509,389, which is assigned to the assignee of my invention.
The transaxle assembly of the '389 patent is adapted to be used with an internal combustion engine mounted in a so-called transverse or "east-west" direction within an engine compartment for a front-wheel drive vehicle. The transaxle includes a hydrokinetic torque converter mounted concentrically with respect to the axis of the engine crankshaft. The turbine of the hydrokinetic torque converter is connected to a torque input shaft for a multiple ratio planetary gear assembly arranged on an axis that is spaced from and parallel to the turbine shaft axis. A torque transfer drive comprising a chain-and-sprocket assembly is adapted to transfer torque from the turbine shaft to the input shaft of a multiple ratio gear system. Fluid pressure operated clutch and brake assemblies are used to establish selectively the various ratios in the gear system to permit adequate torque ratio coverage for the powertrain. A final drive assembly located on the torque output side of the gearing multiplies the output torque of the planetary gearing and delivers it to a differential carrier, the side gears of the carrier being connected to axle half-shafts through universal joints.
An example of a transaxle having a transverse engine is shown in U.S. Pat. No. 4,368,649, which also is assigned to the assignee of this invention.
Arrangements of this kind are referred to in the automotive industry as so-called "U-drives". They usually are found in front-wheel drive vehicles with transversely mounted engines, but they may be adapted also for various other powertrain arrangements for vehicles presently used in the automotive industry. The torque delivered from the transaxle differential assembly in an arrangement of this kind may be transferred to a torque output shaft concentrically disposed within the planetary gearing. The output shaft extends in a transverse direction to the torque input ends of each of the two axle half-shafts for the traction wheels.
Another example of a prior art transaxle and engine assembly is shown in U.S. Pat. No. 4,607,541 wherein the hydrokinetic torque converter is disposed concentrically with respect to the multiple ratio planetary gearing on the axis of the crankshaft of the internal combustion engine. As in the case of the arrangement of the '389 patent, the torque output from the planetary gearing is delivered to a driven shaft coaxially disposed with respect to the planetary gearing. A final drive assembly located between the torque converter and the planetary gearing is adapted to deliver torque to the carrier of a differential assembly. Axle shafts are connected to the side gears of the differential assembly, but these half-shafts are in spaced, parallel disposition with respect to the planetary gearing. This is in contrast to the arrangement of the '389 patent where the axle shafts are coaxially disposed with respect to the planetary gearing.
An example of an engine and transaxle assembly wherein driving axle half-shafts are disposed perpendicularly with respect to the axis of the engine crankshaft is shown in U.S. Pat. No. 4,056,988. In this case, a differential gear assembly has its side gears disposed perpendicularly with respect to the axis of the planetary gearing, the latter being spaced from and parallel to the axis of the engine crankshaft.
Engine and transaxle assemblies of the kind described in the preceding paragraphs require a relatively large engine and transaxle compartment in the vehicle. This restricts the ability of the automotive designer to develop an optimum profile for improved aerodynamics and for reduced vehicle weight. To minimize the space required for the engine and transaxle, and thus increase the space dedicated to the passengers and cargo, attempts have been made to arrange the engine and the transmission gearing with the axis of the engine crankshaft generally perpendicular to the axis of the gearing in a T-drive configuration without a significant offset between the axes. This requires a direct driving connection between the engine crankshaft and the torque input drive for the multiple ratio gearing. An example of an attempt to develop such a configuration is described in an automotive publication entitled "Auto Notizie", published by the Cizeta Moroder Company of Italy, in May 1989. That publication describes a V-16 engine with two independent crankshafts arranged end-to-end. The adjacent ends of the crankshafts are connected to a drive gear, and engine crankshaft torque is delivered through an idler to a bevel gear which serves as a torque input shaft for a multiple ratio transmission having an axis disposed perpendicularly with respect to the crankshaft axis.
Another prior art example of an attempt to locate the transmission axis perpendicularly with respect to the engine crankshaft axis is shown in Japanese Patent Application Publication 56-20861, dated Feb. 26, 1981. That publication shows a drive gear located on one end of an engine crankshaft. The drive gear is connected through a friction clutch to the input shaft of a multiple speed transmission located on an axis parallel to the crankshaft axis. The multiple speed transmission, in turn, is connected to a transversely disposed output shaft that is geared to the torque output shaft of a multiple ratio transmission through torque transfer gearing.
A T-drive arrangement having cross-axis gears located externally of the engine is described in French Patent 933,078, issued Apr. 9, 1948. This disclosure describes a driveline having a neutral clutch located at the torque output side of the cross-axis gearing in a cross-axis housing. The output side of the neutral clutch is connected to a concentric torque input shaft for a multiple ratio transmission. The input side of the transmission is connected to a conventional driveshaft for the rear vehicle wheels. This arrangement has an obvious space penalty in both the transverse direction and the fore-and-aft direction.
Another example of a cross-axis drive somewhat similar to the design of the French patent is shown in U.S. Pat. No. 1,991,575. In the case of the design of the '575 patent, right angle drive bevel gears are located on the torque output side of a neutral clutch for the engine. No attempt is made in the design of either the '575 patent or the French patent to provide a cross-axis drive connection having an integrated engine crankshaft and gearing arrangement.
Each of these prior art teachings of T-drives is characterized by an undesirable complexity because of the additional gearing required to transfer torque from the crankshaft to the input side of the multiple ratio gearing. They are characterized also by an undesirable space penalty which would make it impossible to use such a design approach in a vehicle design that requires a low profile in the forward engine compartment and which requires a maximum cargo and passenger space.